A microbial infection in an organism launches the organism's own, complicated defence mechanisms against the infection. Laboratory tests and clinical investigation of a patient reveal typical changes. Infections, but also traumas, inflammatory processes and cancers cause in an organism changes, which are called acute phase reactions. These changes are called acute, since they appear within a few hours or days from the infection or trauma. The background of the changes lies in the increase of the protein synthesis in liver caused by interleukin 1 and interleukin 6 which are formed as a consequence of the infection or inflammation.
Such proteins of the acute phase include baptoglobin, ceruloplasmin, fibrinogen, amyloid-A and C-reactive protein (CRP). It is most useful to determine CRP in blood, since its concentration increases in connection with an infection, inflammation and tissue damage. The changes in the serum concentration of CRP can increase up to hundredfold. It is also fairly cheap to determine CRP in serum, wherefore CRP has proved a convenient diagnostic tool. The main applications of CRP are detection of infectious diseases and differential diagnostics between bacterial and viral infections. However, in addition to serious bacterial infections, a CRP value can be very high also in invasive viral infections, as e.g. epidemic nephropathy and herpes virus infections of mouth and throat. The concentration of CRP illustrates mainly the invasive character of the infection as well as related tissue damage and the action of inflammatory cells. Consequently, CRP is not as such specific in regard to the source of the infection.
In clinical work CRP is today the most important acute phase protein, because it changes quickly and is suitable for monitoring the inflammatory level of various diseases, and thus also the effect of treatment. CRP concentration can change substantially to either direction even in less than 24 hours. Instead, another commonly used measure of inflammation, Erythrocyte Sedimentation Rate (ESR), changes much slower. It does not increase substantially until one week after the initiation of the inflammation and, correspondingly, its half-time is weeks. In differential diagnostics of infectious diseases ESR alone has no specific value.
In practical clinical work it would be very important to have also other than microbiological means to assess a possible viral or bacterial infection as a cause of the deterioration of the clinical state of a patient. Consequently, a reliable and rapid detection of an infection, or the nature of the infectious agent is important to enable a correct diagnosis. The an appropriate treatment of the infection can be stared as soon as possible, or a proper assessment can be made if anti-inflammatory treatment is necessary at all. A prolonged hospitalising and intravenous antibiotic treatment can thus be avoided.
It is known that different diseases cause changes in the amounts of the leukocyte surface receptors. Such receptors have been studied for instance in atopic and cancer patients. Leino et al. (1997) and Isolauri el al. (1997) have studied the receptor changes in febrile and atopic patients, respectively. However, the knowledge of the receptor changes in such conditions has not been applied to differential diagnostics, nor has such a knowledge been combined with ESR data or the data of chemiluminescence response of whole blood, ie. the level of cell activation, as has been done in the present invention.